Marylene Y. PellosisIV GravitonBiology 3 – Worksheet No.3.1 – The Race to Discover DNA1.What is the Central Dogma of Molecular Biology?-The central dogma of molecular biology deals with the detailed residue-by-residue transfer of sequential information. It states that information cannot be transferred back from protein to either protein or nucleic acid.2.For each of the images (I – IV) describe what this study proved to bacteriologist Frederick Griffith.In 1928, Fred Griffith published a study on the different strains of Pneumococcus, a bacterium that grows in the body of the host, unlike other bacteria, also can be grown on solid or liquid creatures. Two in particular, S and R, look different. The S colonies have a smooth, and the R colonies look rough. The S colonies look smooth because each bacterium has a capsule-like coat made of sugars. This coat protects the S bacteria from the host’s immune system, and so the S strain is infectious. The coat-less R strain is not. Griffith found that mice injected with the S strain develop pneumonia and die within days. Mice injected with the R strain do not get pneumonia.I.II.III.IV.

This
preview
has intentionally blurred sections.
Sign up to view the full version.

Griffith noticed that different strains of Pneumococcus could be cultured from one patient. He began to wonder if one strain could change into another. To test this idea, he did a series of experiments using the R and S strains.First, Griffith heated the S strain culture to kill the bacteria. As predicted, when injected to mice, the heat-killed bacteria did not produce an infection. Griffith co-injected the heat-killed S with live R into mice, and much to his surprise, the mice developed pneumonia and died. Even more astonishing, Griffith was able to isolate live S strain from the blood of infected mice. These cultures could infect other mice. S strain cultured from infected mice remained active – showing that the change was stable and inherited. Griffith concluded that some “principle” was transferred from the heat-killed S to the R strain. The principle transformed the R into the infective S strain with a smooth coat.3.Briefly describe how Avery, McCarty and McLeod further developed Griffiths experiment.Sixteen years later after Griffith’s experiment, the team of Avery, MacLeod and McCarty revisited this experiment and attempted a more definitive experiment. They extracted from Streptococcus pneumoniae S bacteria nucleoid purified DNA, proteins and other materials and mixed R bacteria with these different materials, and only those mixed with DNA were transformed into S bacteria. For their experiments they used a test tube assay instead of mice.

This is the end of the preview.
Sign up
to
access the rest of the document.